1. Field of the Invention
The present invention relates to a method for controlling an exhaust gas purification system and the exhaust gas purification system for performing regeneration control including an exhaust gas temperature rise control accompanied with change of an engine speed of idling in order to recover a purification capacity of an exhaust gas purification device including a Diesel Particulate Filter (DPF) for purifying components in the exhaust gas in an internal combustion engine such as diesel engines.
2. Background Art
Regulations on an amount of the particulate matter (PM) exhausted from a diesel engine as well as NOx, CO, HC and the like have been tightened year by year. A technology has been developed wherein the PM is collected by a DPF to thereby reduce the PM amount exhausted to the outside. A continuous regeneration type DPF device carrying a catalyst is among them.
In this continuous regeneration type DPF device, when an exhaust gas temperature is approximately 350° C. or above, the PM collected by the filter is continuously burned and purified, and the filter is self-regenerated. However, if the exhaust temperature is low, for example, if a low exhaust temperature state such as in an idling operation, a low-load/low-speed operation, or the like of an internal combustion engine continues or the like, a temperature of the exhaust gas is low, and the temperature of the catalyst is lowered and the catalyst is not activated. Thus, oxidation reaction is not promoted, and oxidation of PM to regenerate a filter becomes difficult. Therefore, accumulation of PM on the filter continues, and clogging of the filter progresses. Thus, there emerges a problem of exhaust pressure rise caused by the clogging of the filter.
One of methods to solve such a problem is a regeneration control for forcedly burning and removing the collected PM by forcedly raising the temperature of exhaust gas when an amount of clogging of the filter exceeds a predetermined one. The method for detecting the clogging of the filter includes a method for detecting using a differential pressure at a front and back of the filter, a method for detecting by calculating a PM amount collected from an operation state of the engine from map data, etc. that is set in advance, and obtaining an amount of the accumulated PM, etc.
Then, in this regeneration control, the exhaust gas temperature rise control is conducted to raise a temperature of the exhaust gas flowing into the filter to the temperature or above at which the PM collected by the filter is burned. By this arrangement, the filter temperature is raised so as to burn and remove the PM and the filter is regenerated. This kind of exhaust gas temperature rise control includes methods of fuel injection in a cylinder (in-cylinder) such as multiple injection (multiple-stage delayed injection), or post injection (after-injection).
The multiple injection is a delayed multiple-stage injection in which the fuel is injected into the cylinder in many stages. By this multiple injection, a fuel amount simply burned in the cylinder without generating torque is increased, and the temperature of the exhaust gas exhausted from the cylinder, that is, the temperature of the exhaust gas flowing into an oxidation catalyst device can be raised to a catalyst activation temperature of the oxidation catalyst or above. The post injection is an auxiliary injection injecting at timing further delayed from the multiple injection after main injection in the in-cylinder injection. By this post injection, HC (hydrocarbon) is increased in the exhaust gas exhausted from the cylinder and the HC is oxidized by the oxidation catalyst. By this oxidation, the temperature of the exhaust gas on the downstream of the oxidation catalyst device can be raised.
On the other hand, there is a problem of oil dilution that the HC is mixed with an engine oil (lubricating oil) by the post-injection and dilutes the engine oil. From a viewpoint of a countermeasure to this problem, the forcible regeneration control is performed during idling when a vehicle is stopped and when an operation state is stable. In this control, when the PM is accumulated in a predetermined amount in the filter device, need of regeneration control of the filter device is notified to an operator (driver) by a warning means such as an alarm lamp. When the driver having received the notification stops the vehicle and presses a manual regeneration button, a manual regeneration control is started and the forced regeneration is carried out.
The oxidation catalyst device is provided in a front stage (upstream side) of the filter device in the system. The HC supplied into the exhaust gas by the post-injection is oxidized through this oxidation catalyst device. Thus, the temperature of the exhaust gas at an entrance of the filter device is increased so as to carry out the forcible regeneration.
In the exhaust temperature rise, when the temperature of the exhaust gas is low as in a low speed and low load operation state, first the temperature of the exhaust gas flowing into the oxidation catalyst device is increased not less than the catalyst activation temperature of the oxidation catalyst by performing the multi-injection. Then, after the temperature of the oxidation catalyst reaches not less than the catalyst activation temperature, the post-injection is performed in addition to the multi-injection. The HC is supplied to the oxidation catalyst device by the post-injection while maintaining the temperature of the exhaust gas not less than the catalyst activation temperature by the multi-injection. Because the HC is oxidized by the oxidation catalyst and generates heat, the exhaust gas flows into the filter device at a state of a further higher temperature. The PM accumulated in the filter device is burned by the exhaust gas with such a higher temperature, and removed.
The exhaust gas purification devices shown in Japanese Patent Application Kokai Publication No. 2004-143987 and Japanese Patent Application Kokai Publication No. 2005-155531, for example, have been proposed as this example. In these devices, the exhaust gas is kept warm by increasing the engine speed of the engine more than the engine speed in a normal idling and by throttling exhaust throttle means (exhaust brake), and at the same time, a multi-injection is performed when the temperature of the exhaust gas flowing into the oxidation catalyst device is not more than the oxidation catalyst activation temperature during the manual regeneration. With these operations, the temperature of the exhaust gas flowing into the oxidation catalyst device is increased not less than the oxidation catalyst activation temperature. After that, the forcible regeneration is further carried out through performing the post-injection. Or, the forcible regeneration is carried out by increasing the engine speed of idling based on a detected value of a temperature sensor that detects the catalyst floor temperature, and additionally, by performing exhaust throttling with an exhaust throttle valve and an after injection at the same time.
At this time, increase of the engine speed of idling more than the normal engine speed is performed in order to improve the temperature rise efficiency of the exhaust gas. However, because the engine speed of idling is increased to the same engine speed as that of the multi-injection even when the post-injection is performed in which the exhaust temperature has already been increased to the oxidation catalyst activation temperature by the multi-injection, there have been problems that the fuel efficiency deteriorates due to this idling up and that noise is generated.